1. Field
Aspects of the present invention generally relate to an image processing apparatus, an image processing method, and a non-transitory computer-readable storage medium.
2. Description of the Related Art
Inkjet recording apparatuses are advantageous in being capable of a high-density and high-speed recording operation and adopting a printing scheme that realizes low running cost and a silent operation, and have been commercialized as output apparatuses of various forms. In recent years, inkjet recording apparatuses have been used for printing a photo image of high quality approaching that of a silver halide photo, as well as for printing an office document using plain paper. One of big factors of the increased image quality of inkjet recording is a decrease in granularity of an image, which has been realized by decreasing the size of ink dots and using color materials of a plurality of densities.
One of factors of not being able to obtain a high-quality image through inkjet recording may be density unevenness of an image resulting from variations in ejection characteristics of a recording head. In an inkjet recording apparatus including a plurality of recording elements (nozzles), the ejection characteristics of the individual recording elements vary, and thereby density unevenness may occur in a recorded image. The variations in ejection characteristics of the recording elements are classified into variations in a landing position of ink and variations in an ejection volume, which may result from variations in a heating value of a heater that heats ink, variations in a nozzle aperture, and so forth. Also, the amounts of ink ejected from the individual recording elements may vary due to variations in a heating value of a heater caused by change over time or variations in viscosity of ink caused by a difference in an environment where the apparatus is used.
Head shading correction is available as a method for reducing an influence of variations in ejection characteristics of a recording head. In head shading correction, a test pattern printed by using a recording head is read, and density values of image data corresponding to individual nozzles are corrected so as to reduce density unevenness. Variations in an ejection volume in a recording element array are not always constant, and the ejection volume independently changes in accordance with an ejection history of a recording element. Thus, it is necessary to regularly perform head shading correction in order to maintain an effect of reducing density unevenness.
Japanese Patent Laid-Open No. 2008-87369 describes a technique of frequently performing head shading correction at an initial stage of using a recording head where the recording density is likely to change, and reducing the frequency of head shading correction after the initial stage ends. Specifically, Japanese Patent Laid-Open No. 2008-87369 describes a technique of dividing a region into sub-regions in a nozzle array direction, determining, for each sub-region, whether or not the number of recordings is in the range where the recording density is likely to change at the initial stage of using the recording head, and determining the frequency of head shading correction.
As in the method described in Japanese Patent Laid-Open No. 2008-87369, in the case of calculating the number of recordings in each nozzle group, a method of counting the number of times the recording elements have been actually driven, or a method of counting the number of dots of image data may be used. In this case, if the number of recordings in each nozzle group is counted by using the number of drives in the former method, a large processing load is imposed on a currently available printer system in which nozzles are arranged at high density, which leads to an increase in cost in the entire printer system. On the other hand, in the latter method of counting the number of dots of image data, in the case of recording an image by using a plurality of nozzle groups by performing a plurality of scanning operations as in multipass recording, the total number of dots recorded in all the scanning operations is obtained, but the number dots recorded by each nozzle group is not obtained.